1. Field of the Invention
The invention relates to a spiral staircase with individual steps made of stone, in particular natural stone, arranged on the newel, wherein the step has a reinforcing element.
2. Description of the Prior Art
Many types of spiral staircases are known. For example, from U.S. Pat. No. 1,446,454, a spiral staircase is known wherein the stone steps rest on steel troughs or steel brackets and the steel troughs or steel brackets are connected to the newel. The making of such a spiral staircase with steel troughs or steel brackets is complicated as the steel troughs and brackets must be made separately. The same also applied to spiral staircases with a steel string-board on the outside radius and often also on the inside radius of the spiral stairs, in which case the steel troughs are welded on the inside and outside to the steel string-boards. These constructions require a lot of space and because of complicated welding work are also expensive. Such spiral staircases also always appear extremely heavy.
In addition, from the FR-A 23 17442 a stairs is known, with which the individual steps are set, freely protruding, into the wall, in which case the steps are nevertheless connected to one another by bolts. The steps acquire the required carrying capacity by reinforcing bars that lie in the steps, to which also the bolts are attached which connect the individual steps to one another.
Furthermore, spiral staircases are known, with which the step consists of two horizontally split layers, wherein a reinforcing of fibreglass fabric is glued in between the two layers and wherein the individual steps rest on top of one another by way of bolts.
With these spiral staircases an extraordinary exact manufacture of the individual steps and an accurate installation of the steps is required, as on the one hand no horizontal gap may occur between the individual steps and on the other hand it must be ensured that the last top step rests directly against the end face of the opening in the ceiling.
These spiral staircases are limited to an outside diameter of 200 cm. Furthermore, such staircases can hardly be used outside as due to the effect of frost the risk exists that the two stone layers may come apart in the area of the fiberglass fabric.